Composite materials of the mentioned kind are mostly used as cutting plates for machining operations or as materials resistant to high temperatures. According to the state of the art materials of the above-mentioned kind are produced through the sintering of pressed bodies made of the corresponding mixtures of hard substances and metal powders, or just of metal powders. The sintering takes place in heatable ovens, which for instance are equipped with graphite heating elements, whereby the heating of the samples takes place indirectly by the radiation emitted by the heating elements, as well as by convection or heat conduction. The drawback of this process is in that the selection of the oven atmosphere is limited by the chemical properties of the heating elements. Furthermore the heating of the hard metals, cermets or steel takes place from the outside in and is substantially controlled by the heat conduction capability and the emissivity of the samples. Depending on the heat conductivity of the samples, the variation range of the heating and cooling ratios is strongly limited, and for this reason expensive steps, and apparatus are required for a satisfactory sintering of for instance ultra-fine hard metals.
In the CN 1050908 it has already been proposed to sinter a WC-CO hard metal with 6% by mass and a small addition of 0.5% by mass TaC in a hydrogen atmosphere at 1250.degree. C. for 10 to 20 minutes in a microwave field, but this process seemed to be limited to such bodies which have only a small metal content. In the case of massive metallic bodies it has been specifically stressed that these can practically not be heated by the microwave. Moreover they reflect the irradiation effect even at the surface areas, due to their high electric conductivity and to the occurring eddy currents.